Better Bridge Design Still Needed

The Florida Department of Transportation has conceded that the Seven Mile Bridge that links Marathon with the lower Florida Keys is rusting from within and will require expensive ongoing maintenance.

Built nine years ago to replace an old, narrow and dangerous span, the state`s longest bridge was expected to stand 50 years before corroding to the extent that has already become apparent.

The Seven Mile Bridge was considered a triumph of engineering when it was completed for $45 million in 1982. But its design concept has proven to be much more durable than the materials from which it was built. Both the concrete used in the bridge`s construction and the plastic coating that is supposed to protect its steel girders are deteriorating much faster than anticipated under constant exposure to sun, wind and salt water.

Three other modern bridges along the 110-mile-long Overseas Highway that connects the mainland with Key West are in equally decaying condition. The Niles Channel, Long Key and Indian Key bridges also will require continuing and extensive repairs to avoid being closed to traffic.

State crews will begin $1.5 million worth of work on the Keys bridges this summer. The money will have to be diverted from other bridge projects because the repairs are considered so essential that the Overseas Highway leapfrogged to No. 1 on the DOT`s list of priorities.

Millions more will have to be spent in future years even under the best of circumstances, meaning no destructive hurricanes or marine accidents.

That`s not the way it was supposed to be. The bridges that were replaced by the new spans had stood for more than four decades because they were made the old-fashioned way -- solid enough to support locomotive traffic. The highway and its 42 bridges were built on the foundation of Henry Flagler`s Florida East Coast Railway after a 1935 hurricane destroyed much of the 1912 roadbed.

Indeed, the formidable hulks of the old bridges still stand parallel to the newer spans in many places because removing them would be simply too difficult and expensive. Their rusted and weather-beaten but all-too-concrete presence is an eloquent silent rebuke to the construction methods and materials of our supposedly more enlightened age.